Power plant

ABSTRACT

A power plant includes an internal combustion engine which drives a planetary differential through a lockable hydrostatic torque converter. One of the differential outputs drives a supercharging air compressor, while the other output drives the power plant load through a drive shaft. The two outputs are inter-connected by a variable displacement hydrostatic drive including a pump and a motor. Thus a split path drive through the hydrostatic leg and through the mechanical connection to the output is provided. A controller receives an engine speed signal, a manifold pressure signal and an engine speed setting and provides an output signal to control a variable fuel supply to the engine and another output signal for controlling adjustment of the hydrostatic pump and motor. A governor is responsive to the speed of the load to control lock-up of the torque converter. In operation at high load speeds, the hydrostatic drive leg is locked out, the compressor is idle, and the torque converter is locked up, yielding an overdrive ratio. Higher power demands caused by increases in power plant load will cause activation of the hydrostatic leg to vary the drive ratio and activate the compressor to increase engine power. Upon further increase of the load, the torque converter unlocks, enabling torque multiplication and maintenance of relatively high engine speed for high power output. The effect of this power plant is to provide reserve power in a usable range only, while maintaining engine speed in an optimum power range.

United States Patent 51 May 30, 1972 Wilkinson POWER PLANT [72]Inventor: William H. Wilkinson, Columbus, Ohio [73] Assignee: PerkinsServices N.V., Curacao, Netherlands Antilles [22] Filed: July 24, 1970[21] Appl. No.: 58,011

[52] U.S. Cl ..74/674, 74/675, 74/857, 74/705 [51] Int. Cl ..Fl6h 37/06,B60k 21/00 [58] Field of Search ..74/674, 687, 733, 856-860, 74/705 [56]References Cited UNITED STATES PATENTS 3,442,153 5/1969 Koss ..74/6873,391,584 7/1968 Glarnann ....74/674 3,013,442 12/1961 Fox et 31......74/857 Primary Examiner-Arthur T. McKeon AttorneyGerhardt, Greenlee &Farris [5 7] ABSTRACT A power plant includes an internal combustionengine which drives a planetary differential through a lockablehydrostatic torque converter. One of the differential outputs drives asupercharging air compressor, while the other output drives the powerplant load through a drive shaft. The two outputs are inter-connected bya variable displacement hydrostatic drive including a pump and a motor.Thus a split path drive through the hydrostatic leg and through themechanical connection to the output is provided. A controller receivesan engine speed signal, a manifold pressure signal and an engine speedsetting and provides an output signal to control a variable fuel supplyto the engine and another output signal for controlling adjustment ofthe hydrostatic pump and motor. A governor is responsive to the speed ofthe load to control lock-up of the torque converter. In operation athigh load speeds, the hydrostatic drive leg is locked out, thecompressor is idle, and the torque converter is locked up, yielding anoverdrive ratio. Higher power demands caused by increases in power plantload will cause activation of the hydrostatic leg to vary the driveratio and activate the compressor to increase engine power. Upon furtherincrease of the load, the torque converter unlocks, enabling torquemultiplication and maintenance of relatively high engine speed for highpower output. The effect of this power plant is to provide reserve powerin a usable range only, while maintaining engine speed in an optimumpower range.

27 Claims, 2 Drawing Figures 72 E i 7 5 t CONTROLLER r 5351" L 1 I l 648Z-- I 74 I 1 i l 80]: 5 --7 GOVERNOR 4 I l I I l l 78 1 68 a i l i i 7013 i Z0 27 I with. I g 1 l 22 l l I I I 10 l 62 i I 1 i I I I I ENGINELOAD i I T '-1NTAK E MANIFOLD 16 1 2 i g 1 MOTOR I l I I L f l POWERPLANT This invention relates to power plants and more particularly to apower plant having a selectively controllable split power device toproduce a desired power output characteristic.

In commercial vehicles such as trucks, the usual method of obtaining ahigh power output over a wide range of load speeds is to provide alarge, naturally aspirated engine or a smaller supercharged engine andto provide a multi-speed manually shiftable transmission or an automatictransmission to enable the engine to operate in a relatively high speedand high power outputrange. However, even with multi-speed or automatictransmissions, the optimum engine speed for maximum power output occursonly at as many load speeds as there are transmission speed ratios,since peak power occurs over a relatively narrow range of engine speeds.

With modern traffic conditions, it is necessary that commercial truckshave a grade climbing capability to maintain minimum speeds on grade oninterstate highways and also to enable faster journey times. It is alsonecessary, with heavy traffic conditions, that a truck be able to enteran interstate highway and accelerate to traffic flow speed in theminimum time possible.

In order to provide sufficient reserve power to enable a truck tomaintain reasonable speeds on grades and to provide an accelerationcapability, it has been necessary to use larger displacement engineswhich then cannot operate at full efficiency at part load on levelgrade. By turbo supercharging a smaller engine, the maximum power outputcan be raised within certain limits. However, the reserve poweravailable for grade operations of the vehicle is still limited, sincethe supercharger is driven by exhaust gases.

It has been proposed to provide a constant power power plant having adifferentially driven mechanical supercharger with a split of powerbetween the power plant load and the supercharger. This type of device,sometimes known as a differentially driven engine, has some advantagesover a turbocharged engine in that a high power output can be maintainedover a relatively wide output speed range, because a reduction in loador drive shaft speeds will produce an increased speed of thesupercharger. However, this range is sill limited and some speed changetransmission must still be provided to further increase the speed rangeto practical values. Also, the reserve power available for gradeoperation is limited to the peak engine power which is at a relativelyhigh engine speed.

It is therefore desirable to have a power plant which provides a reservepower capability under the two main conditions when a heavy dutycommercial vehicle such as a truck requires it, i.e. when encounteringgrades and when accelerating to road speeds.

It is an object of this invention to provide a power plant having areserve power capability which is automatically called upon when neededand which maintains engine speeds within a desirable power output range.

It is another object of this invention to provide a power plant whichmaintains a relatively constant engine speed over a wide range of loadspeeds and also causes the engine power output to increase uponincreases in the power plant load.

It is a further object of this invention to provide a power plant whichcan be controlled to operate at low engine speeds up to large fuel/airratios over a wide range of output speeds and also causes the enginepower to increase upon increases in the power plant load by increasingengine speed at large fuel/air ratios.

In carrying out the aforementioned objects, a power plant is providedwhich consists of an air breathing engine having a fuel supply, avariable power splitting device having an input and first and secondoutputs, first connecting means operatively interconnecting the engineand the input, second connecting means operatively interconnecting thefirst output and the load, an auxiliary air device for the engineconnected to the second output, and regulating means for the power plantincluding a controller for automatically controlling the speed ratio ofthe variable power splitting device to vary the power split between theoutputs to cause the power plant to produce a predetermined power outputcharacteristic.

Further, a power plant is provided which consists of an air breathingengine having an intake manifold, characterized by a variable fuelsupply, a differential device having an input and first and secondoutputs, first connecting means operatively interconnecting the engineand the input, second connecting means operatively interconnecting thefirst output and the load, an auxiliary air device for the engineconnected to the second output, variable ratio power transmitting meansconnecting one output with the other output or input, and regulatingmeans for the power plant including a controller for controlling theratio of the variable ratio power transmitting means to control thespeed relationship among the engine, load and auxiliary air device andthereby cause the power plant to produce a predetermined power outputcharacteristic.

This invention provides what may be termed a controllable split pathpower plant.

This invention can be better understood by reference to the followingdetailed description of a preferred embodiment shown in the attacheddrawings wherein:

FIG. 1 is a schematic representation of a power plant according to thisinvention including a control system therefor; and

FIG. 2 is a graphic representation of the characteristics for a specificform of the subject power plant, showing gross horsepower output, pumpdisplacement, motor displacement, engine speed, compressor speed, andpressure ratio plotted against load speed.

Referring now to FIG. 1 of the drawings, an air breathing internalcombustion engine 10, preferably a diesel engine, has an intake manifold12 and is supplied with fuel from a variable fuel supply device 14.These may be mounted in a stationary power plant or in a commercialtruck or other vehicle, not shown. The output shaft 16 of the engine 10drives a variable speed torque transmitting device, preferably ahydrodynamic torque converter 18. A lock-up clutch 20 interconnects theshaft 16 and an impeller 22 with a turbine 24 secured on a shaft 26.

Shaft 26 is the input for a variable power splitting device, generallydenoted 27, which includes a differential device in the form of aplanetary gearset 28. Thus, the torque converter forms connecting meansbetween the engine and the differential. The shaft 26 is connected to aplanet carrier 30 which journals a plurality of planet pinions 32 thatmesh with a sun gear 34 and a ring or internal gear 36. The sun gear 34,which forms one output of the differential, drives a gear 37 through anidler gear 38. Gear 37 is rigidly connected to another gear 40 whichdrives a shaft 42, forming a first output of the variable powersplitting device 27. Shaft 42 drives a supercharging positivedisplacement air compressor 44 which is connected through a bypass 45 tothe manifold 12.

Gear 37 is also rigidly mounted on the input shaft 46 of a conventionalvariable displacement hydrostatic pump device 48. The pump 48 isconventionally connected by hydraulic lines 50 through a reversing valve51 to a variable displacement hydrostatic motor device 52. The outputshaft 54 of motor 52 drives a gear 56 rigidly mounted on a shaft 58through an idler gear 60. The shaft 58 is further rigidly connected tothe ring gear 36 for drive thereby and forms another output for thedifierential. Thus the hydrostatic pump and motor comprise variablepower transmitting means interconnecting two of the differentialmembers. The shaft 58 forms a second output for the variable powersplitting device 27 and is connected at its terminal end with a load 60,which could be the drive wheels, not shown, of a truck.

It is thus seen that the engine 10, through the torque converter 18,drives a variable power splitting device including differential gearing28 which splits the power between a mechanical connection, via ring gear36 directly to the output shaft 58, and a variable hydrostatic leg,comprising pump 48 and motor 52. It is also readily seen that thecompressor 44 is rigidly connected for rotation in response to operationof the hydrostatic pump.

The regulating or control means for the power plant will now bediscussed with reference again to FIG. 1. A governor 64 is adapted toreceive a load speed signal 66 and send out a control signal 68 to acontrol'valve or the like 70 for the torque converter lock-up clutch 20.A controller 72 receives a manifold pressure signal 74 from manifold 12,a speed setting or an input signal 76 from a manually operated operatorscontrol pedal 77, and also an engine speed signal 78. Controller 72sends an output control signal 80 to the fuel supply 14, which alsoreceives the manifold pressure signal 74 from the manifold 12.Controller 72 also sends an output signal 82 directly to a controldevice 84 which regulates the displacements of the hydrostatic pump 48and motor 52 via respective signals 86 and 88.

It is thus seen that the speed of the load controls lock-up of thetorque converter. The control pedal setting, engine speed and manifoldpressure combine to produce a signal to control displacement of thehydrostatic pump and motor and operation of the compressor 44, and alsocontrol the engine fuel supply, as modifiedby sensed manifold pressure,to provide the desired fuel/air ratio.

As previously noted, it is desirable to provide a power plant having areserve power capability which may be used in the two conditions mostcritical for a truck, i.e. upon encountering grades at road speed andduring acceleration to road speed upon entering a highway. By referringnow to FIG. 2, which illustrates the power and component operatingcharacteristics of a specific form of this invention installed in atruck, it will be seen that the subject power plant accomplishes theseobjectives.

In the upper portion of FIG. 2 the abscissa of the graph is calibratedin per cent of cruising road (load) speed for a typical 45,000 lb.G.V.W. truck, while the ordinate measures power plant gross outputhorsepower. The solid line curve denoted 90 shows the maximum poweroutput characteristics of the truck provided with the subject powerplant and will be later described. The chain line curve denoted 95 showsthe maximum power output characteristics of the same truck provided witha power plant comprising a larger naturally aspirated engine, having 40per cent more horsepower than the subject engine 10, and a IO-speedmanual transmission. The dashed gradient lines marked in per cent ofgradient establish the grade climbing capability of both power plants.

It will be noted that in the lower and higher speed ranges, curve 95evidences a greater power output than does curve 90, while in themid-range speeds curve 90 illustrates a superior power outputcapability. It will be seen that a truck having the subject power planthas a greater speed capability on grades between 2 per cent andapproximately 18 per cent than the truck having the larger engine powerplant for this representative example.

The remainder of FIG. 2 graphically describes the operationalcharacteristics of each major component of the subject power plant. Thegraphs B, C, D, E and F respectively plot pump displacement, motordisplacement, engine speed, compressor speed (in all of which 1.0respective maximum displacements, maximum power speed and maximumdesired speed) and manifold pressure (in atmospheres) vs load speed.These graphs will now be explained in conjunction with an operationaldescription of grade climbing ability of the aforementioned truckpowered by the subject power plant.

Referring now to graph A, assume that the truck is traveling along alevel or per cent gradient road where the required power, represented bycurve segment 96-100, is less than the maximum power capability of theengine in overdrive. At these load speeds, represented by the 0 per centdashed gradient curve segment 96-98, governor 64 causes the torqueconverter clutch 20 to be locked up. The less than maximum engine speedrequested of controller 72 by the operator's pedal signal 76 causesmotor 52 to be at 0 per cent displacement and pump 48 to be at 100 percent displacement, as noted in graphs B and C. Even when the operatorinput signal 76 is for a lower engine speed, the above condition isproduced regardless of signal 82, because the hydrostatic adjustrnent isat its highest limit and cannot further adjust. However, in thisinstance the'fuel signal causes the fuel supply 14 to reduce the fuel tothe engine. Whereas operation on a level road at point 96 would be atmaximum fuel/air ratio, operation at point 98 would be at a reducedfuel/air ratio because less power is needed. With the motor 52 at 0 percent displacement, pump 48 provides a stationary reaction for theplanetary differential 28 to produce a purely mechanical overdrivethrough ring gear 36. Since pump 48 is stationary, compressor 44 is notbeing driven, as noted in graph E. During this time the engine isoperating at a fixed relation to load speed and, as noted in graph F, atatmospheric pressure which is provided by the compressor bypass valve45.

As a grade is encountered, the load speed decreases as the loadincreases until controller 72 causes a maximum fuel/air ratio to bedelivered by the fuel supply 14. As the operator senses the reduction inload speed he would operate pedal 77 to increase the engine speedsetting 76. Assuming the pedal 77 is completely depressed, the desiredengine speed setting would be 1.0 and power plant power outputcharacteristics would move from curve segment 96-98 to the correspondingportion of curve 90.

To maintain maximum engine speed, controller 72 effects and increasesdisplacement of motor 52, graph C, which changes the drive ratio to load62 since the hydrostatic leg of the split path power transmission isactuated as pump 48 can now rotate. This also causes compressor 44 torotate and begin to supply some of the air to manifold 12, graph E.

When load speed reaches point 100, motor displacement has increased to0.40, enabling compressor speed to reach 0.50 to supply all the air tomanifold 12 at atmospheric pressure. Thus point 100 may be termed anatmospheric point. Engine speed has been kept at 1.0 (maximum powerspeed) by the changing drive ratio enabled by increased power flowthrough the ratio-changing hydrostatic leg.

In a practical system, system pressures, heat and friction wouldpreclude efficient operation of the hydrostatic leg at small motordisplacements. Thus motor displacement would be held at 0 and thensuddenly increased from 0 to 0.40, as indicated by chain lines96-97-100, graph C. This would cause equivalent compressor operationsimilarly shown in graph E so that all engine air would be supplied bybypass 45 until then. This practical operation would cause engine speed,graph D, to decrease along chain lines 96-97 in proportion to load speeddecrease because of the all-mechanical overdrive. Engine speed wouldthen suddenly increase, 97-100. Chain line curve 96-97-100 on graph Ashows that output power would decrease as engine speed slows from itsmaximum power speed, then suddenly increase. The fuel supply to theslowing engine would be correspondingly decreased, ascontroller 72senses the speed decrease, to maintain the proper fuel/air ratio.

If the grade is sufficiently steep so that output speed decreasesfurther, curve reaches another point 110 which may be termed the peakpower point. Between points and 110, controller 72 gradually increasesmotor displacement to approximately 0.90 which enables the compressor tospeed up to approximately 1.0, yielding a manifold pressure of 2atmospheres. During this time the fuel supply is increased in responseto the sensed increase in manifold pressure, engine speed is maintainedat 1.0 by the changing transmission ratio caused by increased power flowthrough the ratio-changing hydrostatic transmission leg.

As output speed further slows, the power output of the power plantdegrades slightly. At load speeds below point 1 10, a continuation ofthe previous rate of motor displacement change would increase compressorspeed at a constant engine speed and result in amanifold pressure inexcess of 2 atmospheres, a maximum value arbitrarily set because ofengine capabilities of an exemplary engine. To prevent this, controller72 slows the rate of motor displacement change, 110-120 in graph C,which causes the engine to slow as load speed decreases. Because thecompressor speed decreases at a slower rate than engine speed, and dueto speed-sensitive engine breathing characteristics under supercharge, a2 atmosphere manifold pressure will be maintained. Controller 72 adjuststhe fuel supply 14 to maintain optimum fuel/air ratio. Thus, sinceengine speed decreases from the maximum power speed at constantsupercharge, output power will decrease, 110-120 in graph A. At point120, termed the crossover point, motor displacement reaches and ismaintained at 1.0 while controller 72 decreases the pump displacement toprovide further variation of the transmission ratio. The rate of pumpdisplacement change is controlled to further decrease respective engineand compressor speeds to 0.75 and 0.80 to maintain the constantsupercharge, 120-130 in graphs A, D, E and F.

At point 130, termed the unlock point, governor 64 unlocks torqueconverter clutch 20, causing an increase from 0.75 to 0.95 inenginespeed, graph D, as the converter is actuated at its coupling point whereit slips. The sudden increase in engine speed causes a drop in manifoldpressure which is sensed by controller 72. To increase manifold pressureto 2 atmospheres, controller 72 suddenly decreases pump displacementwhich increases pump speed and compressor speed, graphs B and E. Thefuel supply is adjusted to accommodate increased engine speed.

At output speeds below point 130, the torque converter allows the engineto remain at a high power output speed because of increasing slip andalso provides torque multiplication. To limit the supercharge, pumpdisplacement is decreased at a predetermined rate causing slightreductions in engine and compressor speeds until the pump displacementreaches 0.40, a practical limit for the same reasons discussed abovewith regard to the motor at 96-97-100 in graph E, at a limit ofadjustment point 140.

As the load speed decreases below point 140, the hydrostatictransmission leg can be adjusted no further. The engine speed willthereafter slowly decrease to approximately 0.60 at a second atmosphericpoint, denoted 150, because the torque converter slips. As the loadspeed continues to slow as the load increases, the compressor speeddecreases in proportion to load speed and an increasing proportion ofair for the engine is supplied through the compressor bypass valve tomaintain the naturally aspirated condition of the engine. The powercurve 90 then diminishes to at a load speed of 0, while engine speeddecreases to 0.60 as defined by the stall characteristics of the torqueconverter.

The comparative power output over the same load speed range by the powerplant having a 40 per cent larger naturally aspirated engine with tenspeed transmission is seen by inspection of curve 95 and the comparisonwill indicate the dramatic advantage of the subject power plant. Forexample, on a 3 per cent grade the subject power plant can maintain aload speed of approximately 77 per cent of cruising speed, while thelarger engine power plant can maintain a speed of only 68 per cent. Moresignificantly, on a 5 per cent grade the subject power plant canmaintain a load speed of 60 per cent while the other power plant canmaintain a speed of only 48 per cent.

Thus the subject power plant can utilize a much smaller displacementengine than previously known and still maintain a significant reservepower for hill climbing capabilities. With more power available fromapproximately the 12-80 per cent of cruising speed range, it will bereadily understood that a dramatically improved acceleration capabilityis achieved.

This is particularly significant for a commercial truck entering a levelgrade, limited access highway where rapid acceleration to a minimumtraffic speed is necessary.

The acceleration characteristics from 0 load speed for the truck poweredby the subject power plant are just the reverse of the grade climbingcharacteristics described above, but will be explained briefly forpurposes of clarification. Full depression of the pedal 77 has nohydrostatic effect because controller 72 has already reduced the pump 48to its minimum displacement. The fuel control 14 however, would becontrolled to deliver maximum fuel/air ratio to engine 10. The enginespeed initially is at 0.60 which is enabled by the torque converterstall characteristic. Similarly the manifold pressure is at atmospheric,the compressor speed at 0, the pump displacement at 0.40 and the motordisplacement at 1.0. The drive is now primarily through the hydrostaticleg. As the load speed increases, the compressor speed increases inproportion while the torque converter holds the engine at nearlyconstant speed. At first the compressor merely supplies an increasingportion of the naturally aspirated air needed by the engine buteventually it begins to create a net supercharge. As the load speeds upfurther the compressor continues to speed up and the engine now beginsto increase in speed until the limiting supercharge is achieved at thelimit of adjustment point 140. At this point engine speed and compressorspeed are at 0.90 and the pump displacement is at 0.40. Thereafter pumpdisplacement is increased by controller 72, which increases compressorspeed slightly to 0.95, and the engine speed similarly increases to0.95.

At point 130 the torque converter is locked up by governor 64, causing adrop in engine speed which increases manifold pressure and causescontroller 72 to suddenly increase the displacement of pump 48. Thisreduces both compressor and engine speeds to 0.75, and maintainsmanifold pressure at 2 atmospheres. After the lock up of the torqueconverter, controller 72 increases pump displacement, which continues torise to crossover point 120, after which the pump is maintained at fulldisplacement and the motor displacement is decreased. During thisperiod, the engine speed and the compressor speed are increased to peakpower point 1 10.

To change the drive ratio to the load, motor displacement continues todecrease, causing a greater portion of the drive to be through thedirect mechanical connection, thereby decreasing compressor speed andmanifold pressure. This causes a drop-off in power at a point beyond 70per cent of cruising speed where great reserve power is not necessary.The power plant continues to operate in the mode described until theatmospheric point 100 is reached at approximately per cent of cruisingspeed. The motor displacement is then, as previously noted, eithersharply or gradually reduced from 0.40 to 0, thereby shifting to acompletely mechanical overdrive which causes a drop of compressor speedto 0. The engine then operates naturally aspirated and the compressor isbypassed.

The subject power plant also has provision for a simple low speedreverse. By operating valve 51 to reverse the direction of flow betweenpump 48 and motor 52, the motor will reverse its direction of rotation.In this mode of operation the hydrostatic output torque overcomes theopposing mechanical torque and produces reverse rotation of shaft 58.

Another feature of the subject power plant is the inherent availabilityof overrun or dynamic braking which is useful for a truck descending agrade. The load will power both the ring gear 36 through shaft 58 andthe sun gear 34 through the hydrostatic leg. This causes motoring ofengine 10. Although drag transmitted across the torque converter issmall, braking effect is contributed by hydraulic losses in thehydrostatic leg and compressor power absorption which causes compressor44 to blow over the engine for cooling purposes. This blowing over" alsoprovides a tow-start capability for engine 10.

This invention provides a complete power plant with engine, transmissionand controls, all interrelated and interacting to produce a desiredpredetermined power output characteristic. Whereas differentiallysupercharged engines, torque converters, and split path transmissionsare well known in the prior art, they have not heretofore been assembledin such an interrelated manner to provide such a power plant. Eachelement of the subject power plant has plural functions which affect andare affected by the other elements. The hydrostatic leg provides acontrollable variable ratio transmission, while enabling desirable highpower output engine speed and regulating compressor speed to control themanifold pressure. The differential enables a speed split betweencompressor and load and also a power transmission split betweenmechanical and hydrostatic. The torque converter enables torquemultiplication at low road speeds so that it can slip efficiently topermit high engine speeds without excessive supercharge. The variouscontrols sense actual and desired operating characteristics and regulateoperation of the elements to optimize operation of the power plant.

Of course, equivalent elements may be used for those specificallydetailed herein without departing from the scope of the invention. Themechanical differential could be replaced with a different mechanical,hydraulic or electrical one. The hydrostatic leg could be mechanical,electrical or hydrodynamic. The torque converter could be a mechanical,hydraulic or electrical device. The compressor could be of a type otherthan positive displacement. The engine could be spark-ignition. Thecontrols could take different form. These are merely some of thealternatives envisaged within the scope of this invention which couldyield a power plant having the same or similar power outputcharacteristics and which are contemplated within the scope of thefollowing claims.

I claim:

1,. A power plant for driving a load, including an air breathing enginehaving a fuel supply, characterized by a variable power splitting devicehaving an input and first and second outputs, first connecting meansoperatively interconnecting the engineand the input, second connectingmeans operatively interconnecting the first output and the load, anauxiliary air device for the engine connected to the second output, andregulating means for the power plant including a controller forautomatically controlling the speed ratio of the variable powersplitting device to vary the power split between the outputs to causethe power plant to produce a predetermined power output characteristic.

2. A power plant according to claim 1, wherein the controller includes amanual input and is responsive to both the manual input and to a speedcondition of the power plant to control the variable power splittingdevice.

3. A power plant according to claim 2, wherein the controller is alsoresponsive to a second speed condition of the power plant.

4. A power plant according to claim 3, wherein the speed conditions areengine speed and second connecting means speed.

5. A power plant for driving a load, including an air breathing enginehaving an intake manifold, characterized by a variable fuel supply, adifferential device having an input and first and second outputs, firstconnecting means operatively interconnecting the engine and the input,second connecting means operatively interconnecting the first output andthe load, an auxiliary air device for the engine connected to the secondoutput, variable ratio power transmitting means connecting one outputwith the other output or input, and regulating means for the power plantincluding a controller for controlling the ratio of the variable ratiopower transmitting means to control the speed relationship among theengine, load and auxiliary air device and thereby cause the power plantto produce a predetermined power output charac teristic.

6. A power plant according to claim 5, wherein the variable thedisplacement of the variable displacement hydrostatic device.

9. A power plant according to claim 7, wherein the regulating meansinclude control valve means for enabling reversing rotation of thehydrostatic motor device to effect reverse rotation of the secondconnecting means and resultant reverse drive of the load.

10. A power plant according to claim 6, wherein the controller isresponsive to a speed condition of the power plant to control thevariable ratio power transmitting means.

11. A power plant according to claim 10, wherein the speed condition isthe speed of the engine.

12. A power plant according to claim 11, wherein the regulating meansinclude a manually adjustable control for the controller and thecontroller is also responsive to the manually adjustable control and tomanifold pressure control to selectively control both the variable fuelsupply and the variable ratio power transmitting means.

13. A power plant according to claim 12, wherein the variable fuelsupply is controlled by the controller and is responsive to intakemanifold pressure to regulate the fuel supplied to the engine.

14. A power plant according to claim 6, wherein the first connectingmeans include a hydrodynamic torque transmitting device.

15. A power plant according to claim 14, wherein the controller isresponsive to a first speed condition of the power plant for controllingthe variable ratio power transmitting means, and the regulating meansinclude a governor responsive to a second speed condition of the powerplant to control the hydrodynamic torque transmitting device to allowthe engine speed to increase above the input speed when the second speedis below a predetermined value.

16. A power plant according .to claim 15, wherein the hydrodynamictorque transmitting device has lock-up means, and the second speed issecond connecting means speed to which the governor is responsive tocontrol the lock-up means.

17. A power plant according to claim 16, wherein the regulating meansinclude a manually adjustable control for the controller, the firstspeed is engine speed, and the controller is responsive to the manuallyadjustable control, to engine speed and to manifold pressure toselectively control both the variable fuel supply and the variable ratiopower transmitting means.

18. A power plant according to claim 17, wherein the variable fuelsupply is controlled by the controller and is responsive to intakemanifold pressure to regulate the fuel supplied to the engine.

19. A power plant according to claim 5, wherein one of the connectingmeans include a variable speed torque transmitting device.

20. A power plant according to claim 19, wherein the variable speedtorque transmitting device is included in the first connecting means.

21. A power plant according to claim 20, wherein the variable speedtorque transmitting device is a hydrodynamic torque converter havinglock-up means.

22. A power plant according to claim 21, wherein the regulating meansinclude a governor responsive to the speed of the second connectingmeans for controlling the lock-up means.

23. A power plant according to claim 5, wherein the auxiliary air devicecomprises a positive displacement air compressor and the controller isresponsive to the intake manifold pressure to control the variable ratiopower transmitting means to limit the intake manifold pressure to apredetermined value.

24. A power plant according to claim 5, wherein the differential deviceincludes planetary gearing having a sun gear connected to the secondconnecting means, a ring gear connected to the auxiliary air device, anda planet carrier connected to the first connecting means.

25. A power plant for driving a load, including an air breathing enginehaving an intake manifold, characterized by a variable fuel supply, adifferential device having an input and first and second outputs, ahydrodynamic torque converter with lock-up means operativelyinterconnecting the engine and the input, connecting means operativelyinterconnecting the first output and the load, an auxiliary air devicefor supercharging the engine connected to the second output, a variabledisplacement hydrostatic device interconnecting the second and firstoutputs, and regulating means for controlling both the torque converterlock-up means and the hydrostatic device displacement and beingresponsive to load speed and engine speed to cause torque converterlock-up and cause the hydrostatic device to stop the second output andthus the auxiliary air device to cause drive of the load solely by thefirst output above a predetermined load speed, and as load speeddecreases to successively vary the displacement of the hydrostaticdevice to progressively increase the speed of the second output and thusthe auxiliary air device to provide engine supercharge and a variableratio split path drive to the load by both outputs and thereafter tounlock the torque converter to enable engine speeds greater than inputspeeds and concurrent torque multiplication.

26. A power plant according to claim 25, wherein the regulating meansare also responsive to intake manifold pressure and are operable toprovide optimum fuel supply and to limit intake manifold pressure to apredetermined value.

27. A power plant according to claim 26, including a manual control forthe regulating means to modify control of the hydrostatic devicedisplacement by the regulating means.

1. A power plant for driving a load, including an air breathing enginehaving a fuel supply, characterized by a variable power splitting devicehaving an input and first and second outputs, first connecting meansoperatively interconnecting the engine and the input, second connectingmeans operatively interconnecting the first output and the load, anauxiliary air device for the engine connected to the second output, andregulating means for the power plant including a controller forautomatically controlling the speed ratio of the variable powersplitting device to vary the power split between the outputs to causethe power plant to produce a predetermined power output characteristic.2. A power plant according to claim 1, wherein the controller includes amanual input and is responsive to both the manual input and to a speedcondition of the power plant to control the variable power splittingdevice.
 3. A power plant according to claim 2, wherein the controller isalso responsive to a second speed condition of the power plant.
 4. Apower plant according to claim 3, wherein the speed conditions areengine speed and second connecting means speed.
 5. A power plant fordriving a load, including an air breathing engine having an intakemanifold, characterized by a variable fuel supply, a differential devicehaving an input and first and second outputs, first connecting meansoperatively interconnecting the engine and the input, second connectingmeans operatively interconnecting the first output and the load, anauxiliary air device for the engine connected to the second output,variable ratio power transmitting means connecting one output with theother output or input, and regulating means for the power plantincluding a controller for controlling the ratio of the variable ratiopower transmitting means to control the speed relationship among theengine, load and auxiliary air device and thereby cause the power plantto produce a predetermined power output characteristic.
 6. A power plantaccording to claim 5, wherein the variable ratio power transmittingmeans is located between the first and second outputs.
 7. A power plantaccording to claim 6, wherein the variable ratio power transmittingmeans include a hydrostatic fluid pump device driven by the secondoutput and a hydrostatic fluid motor device driven by the pump deviceand connected to the first output, at least one of the hydrostaticdevices having a variable displacement controlled by the controller. 8.A power plant according to claim 7, wherein the controller is responsiveto the speed of the engine for controlling the displacement of thevariable displacement hydrostatic device.
 9. A power plant according toclaim 7, wherein the regulating means include control valve means forenabling reversing rotation of the hydrostatic motor device to effectreverse rotation of the second connecting means and resultant reversedrive of the load.
 10. A power plant according to claim 6, wherein thecontroller is responsive to a speed condition of the power Plant tocontrol the variable ratio power transmitting means.
 11. A power plantaccording to claim 10, wherein the speed condition is the speed of theengine.
 12. A power plant according to claim 11, wherein the regulatingmeans include a manually adjustable control for the controller and thecontroller is also responsive to the manually adjustable control and tomanifold pressure control to selectively control both the variable fuelsupply and the variable ratio power transmitting means.
 13. A powerplant according to claim 12, wherein the variable fuel supply iscontrolled by the controller and is responsive to intake manifoldpressure to regulate the fuel supplied to the engine.
 14. A power plantaccording to claim 6, wherein the first connecting means include ahydrodynamic torque transmitting device.
 15. A power plant according toclaim 14, wherein the controller is responsive to a first speedcondition of the power plant for controlling the variable ratio powertransmitting means, and the regulating means include a governorresponsive to a second speed condition of the power plant to control thehydrodynamic torque transmitting device to allow the engine speed toincrease above the input speed when the second speed is below apredetermined value.
 16. A power plant according to claim 15, whereinthe hydrodynamic torque transmitting device has lock-up means, and thesecond speed is second connecting means speed to which the governor isresponsive to control the lock-up means.
 17. A power plant according toclaim 16, wherein the regulating means include a manually adjustablecontrol for the controller, the first speed is engine speed, and thecontroller is responsive to the manually adjustable control, to enginespeed and to manifold pressure to selectively control both the variablefuel supply and the variable ratio power transmitting means.
 18. A powerplant according to claim 17, wherein the variable fuel supply iscontrolled by the controller and is responsive to intake manifoldpressure to regulate the fuel supplied to the engine.
 19. A power plantaccording to claim 5, wherein one of the connecting means include avariable speed torque transmitting device.
 20. A power plant accordingto claim 19, wherein the variable speed torque transmitting device isincluded in the first connecting means.
 21. A power plant according toclaim 20, wherein the variable speed torque transmitting device is ahydrodynamic torque converter having lock-up means.
 22. A power plantaccording to claim 21, wherein the regulating means include a governorresponsive to the speed of the second connecting means for controllingthe lock-up means.
 23. A power plant according to claim 5, wherein theauxiliary air device comprises a positive displacement air compressorand the controller is responsive to the intake manifold pressure tocontrol the variable ratio power transmitting means to limit the intakemanifold pressure to a predetermined value.
 24. A power plant accordingto claim 5, wherein the differential device includes planetary gearinghaving a sun gear connected to the second connecting means, a ring gearconnected to the auxiliary air device, and a planet carrier connected tothe first connecting means.
 25. A power plant for driving a load,including an air breathing engine having an intake manifold,characterized by a variable fuel supply, a differential device having aninput and first and second outputs, a hydrodynamic torque converter withlock-up means operatively interconnecting the engine and the input,connecting means operatively interconnecting the first output and theload, an auxiliary air device for supercharging the engine connected tothe second output, a variable displacement hydrostatic deviceinterconnecting the second and first outputs, and regulating means forcontrolling both the torque converter lock-up means and the hydrostaticdevice displacement and being responsive to load speed and engine speedto cause torque converter loCk-up and cause the hydrostatic device tostop the second output and thus the auxiliary air device to cause driveof the load solely by the first output above a predetermined load speed,and as load speed decreases to successively vary the displacement of thehydrostatic device to progressively increase the speed of the secondoutput and thus the auxiliary air device to provide engine superchargeand a variable ratio split path drive to the load by both outputs andthereafter to unlock the torque converter to enable engine speedsgreater than input speeds and concurrent torque multiplication.
 26. Apower plant according to claim 25, wherein the regulating means are alsoresponsive to intake manifold pressure and are operable to provideoptimum fuel supply and to limit intake manifold pressure to apredetermined value.
 27. A power plant according to claim 26, includinga manual control for the regulating means to modify control of thehydrostatic device displacement by the regulating means.